The present invention relates to a permeable composite material having ion-conducting properties.
Ion-conducting materials of the prior art are in service in very broad scope in technology and are used for the most diverse applications. In this context there could be cited in particular not only the applications in electrodialysis as anion or cation exchange membranes but also the application as diaphragms in electrolysis or membrane-electrolysis cells as well as the membrane in pervaporation modules. Further fields of application can be found in the area of energy production with fuel cells. There is also known, however, an entire series of electrochemical or catalyzed reactions which take place on ion-conducting materials or are catalyzed thereby.
At present, predominantly polymer materials bearing ionic groups are used for these applications. The modified polysulfones, polyether sulfones, polystyrenes and modified polyvinylidine fluoride and polytetrafluoroethylene in particular could be cited in this context. These materials have performances completely adequate for most applications. Nevertheless, these polymers are subject to limits as regards the temperature range in which they can be used. At a temperature of about 120xc2x0 C. or above, for example, either softening of the material occurs or the materials are no longer sufficiently swellable to ensure good ion conduction.
Inorganic materials such as zeolites or other aluminosilicates are indeed characterized by better thermal stability, but frequently are not sufficiently stable in acid media, with the result that slow decomposition of the materials takes place during operation. Thus they also have fields of application only in a limited area, such as in the sodium sulfide/sulfur cell (energy storage) or in some electrolysis apparatuses.
PCT/EP98/05939 describes a permeable composite material and a process for making the same. This permeable composite material is characterized by high thermal stability, but it lacks ion-conducting properties.
The purpose of the present invention was to find a material which still has good ion conduction even at temperatures of up to 250xc2x0 C. and which at the same time is insensitive to relatively high acid concentrations.
It has been surprisingly found that it is possible to impart ion-conducting properties to a permeable composite material based on at least one porous and permeable support, which is provided on at least one side of the support and in the interior of the support with at least one inorganic component, which contains substantially at least one compound of a metal, a semi-metal or a mixed metal with at least one element of Group 3 to Group 7, while retaining its good thermal stability and resistance to acids.
The subject matter of the present invention is therefore a permeable composite material based on at least one porous and permeable support, which is provided on at least one side of the support and in the interior of the support with at least one inorganic component, which contains substantially at least one compound of a metal, a semi-metal or a mixed metal with at least one element of Group 3 to Group 7, which composite material is characterized in that it exhibits ion-conducting properties.
Also subject matter of the present invention is a process for making a composite material based on at least one porous and permeable support, which is provided on at least one side of the support and in the interior of the support with at least one inorganic component, which contains substantially at least one compound of a metal, a semi-metal or a mixed metal with at least one element of Group 3 to Group 7, which process is characterized in that a composite material with ion-conducting properties is made.
Further subject matter of the present invention is the use of a composite material according to at least one of claims 1 to 20 as a catalyst for acid or base catalyzed reactions.
The ion-conducting composite material according to the invention is characterized by good ion-conducting properties. Contrary to the general assumption that materials having good ion conduction must be pore-free, it has been found that materials having good ion conduction do not absolutely have to be pore-free, but instead the pore size merely has to be smaller than a certain limit value. If the pore surfaces contain ionogenic groups, ion conduction takes place in the form of a surface diffusion mechanism. Provided the porosity is quite high, this mechanism of ion migration leads to high ion fluxes through the material, so that current densities of greater than 50 mAxc2x7cmxe2x88x922 can be achieved.
Not only good conductivity but also the greatest possible permselectivity is necessary for use of membranes in electrodialysis or as a proton-conducting membrane in fuel cells. This requirement is also thoroughly satisfied by the composite material according to the invention. The permselectivities of the ion-conducting composite materials according to the invention and used as membrane materials lie in the range of 0.75 to 0.98 depending on the material used.
The composite material according to the invention will be described hereinafter by reference to an example, without being limited thereto.
The permeable composite material according to the invention based on at least one porous and permeable support, which on at least one side of the support and in the interior of the support is provided with at least one inorganic component, which substantially contains at least one compound of a metal, a semi-metal or a mixed metal with at least one element of Group 3 to Group 7, exhibits ion-conducting properties. As used in the present invention, the term interior of a support refers to cavities or pores in a support.
According to the invention, the porous and permeable support can have interstices with a size of 0.02 to 500 xcexcm. The interstices can be pores, meshes, holes, crystal lattice interstices or cavities. The support can contain at least one material chosen from carbon, metals, alloys, glass, ceramics, minerals, plastics, amorphous substances, natural products, composite substances or from at least one combination of these materials. It is permissible for supports which can contain the said materials to have been modified by a chemical, thermal or mechanical treatment method or a combination of treatment methods. Preferably the composite material is provided with a support which contains at least one metal, one natural fiber or one plastic, which was modified by at least one mechanical forming technique or treatment method, such as drawing, upsetting, fulling, rolling, stretching or forging. Quite particularly preferably the composite material is provided with at least one support which contains at least woven, bonded, felted or ceramically bound fibers or at least sintered or bonded shapes, globules or particles. In a further preferred embodiment there can be used a perforated support. Permeable supports can also be such which become or have been made permeable by laser treatment or ion beam treatment.
It can be advantageous if the support contains fibers of at least one material chosen from carbon, metals, alloys, ceramics, glass, minerals, plastics, amorphous substances, composite substances and natural products or fibers of at least one combination of these materials, such as asbestos, glass fibers, carbon fibers, metal wires, steel wires, steel-wool fibers, polyamide fibers, coconut fibers, coated fibers. Preferably there are used supports containing woven fibers of metal or alloys. Wires can also be used as metal fibers. Quite especially preferably the composite material is provided with a support which contains at least one fabric of steel or stainless steel, such as a fabric made by weaving from steel wires, steel fibers, stainless-steel wires or stainless-steel fibers, which fabric preferably has mesh widths of 5 to 500 xcexcm, especially preferably mesh widths of 50 to 500 xcexcm, and quite especially preferably mesh widths of 70 to 120 xcexcm.
The support of the composite material, however, can also comprise at least one expanded metal with a pore size of 5 to 500 xcexcm. According to the invention, however, the support can also comprise at least one granular, sintered metal, one sintered glass or one metal fleece with a pore width of 0.1 xcexcm to 500 xcexcm, preferably of 3 to 60 xcexcm.
The composite material according to the invention is preferably provided with at least one support which contains at least aluminum, silicon, cobalt, manganese, zinc, vanadium, molybdenum, indium, lead, bismuth, silver, gold, nickel, copper, iron, titanium, platinum, stainless steel, steel, brass, an alloy of these materials or a material coated with Au, Ag, Pb, Ti, Ni, Cr, Pt, Pd, Rh, Ru and/or Ti.
The inorganic component present in the composite material according to the invention can contain at least one compound of at least one metal, semi-metal or mixed metal with at least one element of Group 3 to Group 7 of the Periodic Table or at least one mixture of these compounds. The compounds of the metals, semi-metals or mixed metals can therefore contain at least elements of the subgroups and of Group 3 to Group 5 or at least elements of the subgroups or of Group 3 to Group 5, these compounds having a particle size of 0.001 to 25 xcexcm. Preferably the inorganic component contains at least one compound of an element of Subgroup 3 to Subgroup 8 or at least one element of Group 3 to Group 5 with at least one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, Al or B or at least one compound of an element of Subgroup 3 to Subgroup 8 and at least one element of Group 3 to Group 5 with at least one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, Al or B or a mixture of these compounds. Especially preferably the inorganic component contains at least one compound of at least one of the elements Sc, Y, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb or Bi with at least one of the elements Te, Se, S, O, Sb, As, P, N, C, Si, Ge or Ga, such as TiO2, Al2O3, SiO2, ZrO2, Y2O3, BC, SiC, Fe3O4, SiN, SiP, nitrides, sulfates, phosphides, silicides, spinels or yttrium aluminum garnet, or of one of these of the elements themselves. The inorganic component can also contain aluminosilicates, aluminum phosphates, zeolites or partly exchanged zeolites, such as ZSM-5, Na ZSM-5 or Fe ZSM-5 or amorphous microporous mixed oxides, which can contain up to 20% nonhydrolyzable organic compounds, such as vanadium oxide silica glass or alumina silica methylsilicon sesquioxide glasses.
Preferably at least one inorganic component is present in a particle-size fraction with a particle size of 1 to 250 nm or with a particle size of 260 to 10,000 nm.
It can be advantageous if the composite material according to the invention contains at least two particle-size fractions of at least one inorganic component. Likewise it can be advantageous if the composite material according to the invention contains at least two particle-size fractions of at least two inorganic components. The particle-size ratio can range from 1:1 to 1:10,000, preferably from 1:1 to 1:100. The quantitative ratio of the particle-size fractions in the composite material can preferably range from 0.01:1 to 1:0.01.
The permeability of the composite material according to the invention is limited by the particle size of the at least one inorganic component used to particles with a particular maximum size.
The composite material according to the invention is characterized in that it has ion-conducting properties and that in particular it is ion-conducting at a temperature of from xe2x88x9240xc2x0 C. to 300xc2x0 C., preferably from xe2x88x9210xc2x0 C. to 200xc2x0 C.
The composite material contains at least one inorganic and/or organic material which exhibits ion-conducting properties. This material can be present as an admixture in the microstructure of the composite material. It can also be advantageous, however, if the interior and/or exterior surfaces of the particles present in the composite material are coated with a layer of an inorganic and/or inorganic material.
Such layers have a thickness of 0.0001 to 1 xcexcm, preferably a thickness of 0.001 to 0.05 xcexcm.
In a particular embodiment of the ion-conducting composite material according to the invention, there is present in the void volume of the composite material at least one inorganic and/or organic material which exhibits ion-conducting properties. This material fills the void volume completely or partly, preferably completely. In particular, at least one inorganic and/or organic material which exhibits ion-conducting properties fills the interstices of the composite material.
It can be advantageous if the material which exhibits ion-conducting properties contains ionic groups from the group of alkylsulfonic acid, sulfonic acid, phosphoric acid, alkylphosphonic acid, dialkylphosphinic acid, carboxylic acid, tetraorganylammonium, tetraorganylphosphonium groups or mixtures of these groups with the same charge. These ionic groups can be organic compounds bound chemically and/or physically to inorganic particles. Preferably the ionic groups are bound via aryl and/or alkyl chains to the interior and/or exterior surface of the particles present in the composite material.
The ion-conducting material of the composite material can also be an organic ion-conducting material, such as a polymer. Especially preferably this polymer is a sulfonated polytetrafluoroethylene, a sulfonated polyvinylidene fluoride, an aminolyzed polytetrafluoroethylene, an aminolyzed polyvinylidene fluoride, a sulfonated polysulfone, an aminolyzed polysulfone, a sulfonated polyether imide, an aminolyzed polyether imide or a mixture of these polymers.
As inorganic ion-conducting materials there can be present in the composite material at least one compound from the group of oxides, phosphates, phosphides, phosphonates, sulfates, sulfonates, vanadates, stannates, plumbates, chromates, tungstates, molybdates, manganates, titanates, silicates, aluminosilicates and aluminates or mixtures of these compounds at least of one of the elements Al, K, Na, Ti, Fe, Zr, Y, Va, W, Mo, Ca, Mg, Li, Cr, Mn, Co, Ni, Cu or Zn or a mixture of these elements.
As inorganic ion-conducting materials, however, there can also be present at least one partly hydrolyzed compound from the group of oxides, phosphates, phosphites, phosphonates, sulfates, sulfonates, vanadates, stannates, plumbates, chromates, tungstates, molybdates, manganates, titanates, silicates, aluminosilicates and aluminates or mixtures of these compounds at least of one of the elements Al, K, Na, Ti, Fe, Zr, Y, Va, W, Mo, Ca, Mg, Li, Cr, Mn, Co, Ni, Cu or Zn or a mixture of these elements. As the inorganic ion-conducting material, preferably there is present in the ion-conducting composite material according to the invention at least one amorphous and/or crystalline compound at least of one of the elements Zr, Si, Ti, Al, Y or vanadium, or silicon compounds bearing some nonhydrolyzable groups, or mixtures of these elements or compounds.
The ion-conducting composite material according to the invention can be flexible. Preferably the ion-conducting composite material is bendable to a minimum radius of as small as 1 mm.
The process according to the invention for making an ion-conducting composite material will be described hereinafter with reference to an example, without limiting the process according to the invention to such production.
The ion-conducting permeable composite materials can be made in various ways. On the one hand, a composite material can be made using ion-conducting materials or materials which exhibit ion-conducting properties after a further treatment. On the other hand, composite materials which are already permeable can be treated with ion-conducting materials or with materials which exhibit ion-conducting properties after a further treatment.
The process according to the invention for making a composite material which exhibits ion-conducting properties relies on a process for making a composite material based on at least one porous and permeable support, which is provided on at least one side of the support and in the interior of the support with at least one inorganic component, which contains substantially at least one compound of a metal, a semi-metal or a mixed metal with at least one element of Group 3 to Group 7. This production process is described in detail in PCT/EP98/05939.
In this process for making the composite material, at least one suspension containing at least one inorganic component comprising at least one compound of at least one metal, one semi-metal or one mixed metal with at least one of the elements of Group 3 to Group 7 is applied in and on at least one porous and permeable support, and the suspension is solidified on or in or on and in the support material by at least one heat treatment.
In this process it can be advantageous to apply the suspension on and in or on or in at least one support by forcing on, pressing on, pressing in, rolling on, doctoring on, spreading on, dipping, spattering or pouring on.
The porous and permeable support on which or in which or on which and in which at least one suspension is applied can contain at least one material chosen from carbon, metals, alloys, ceramics, minerals, plastics, amorphous substances, natural products, composite substances, composite materials or from at least one combination of these materials. As the permeable support there can also be used such made permeable by treatment with laser beams or ion beams. Preferably fabrics of fibers or wires of the materials cited hereinabove are used as supports, examples being metal fabrics or plastic fabrics.
The suspension used, which can contain at least one inorganic component and at least one metal oxide sol, at least one semi-metal oxide sol or at least one mixed metal oxide sol or a mixture of these sols, can be prepared by suspending at least one inorganic component in at least one of these sols.
The sols are obtained by hydrolyzing at least one compound, preferably at least one metal compound, at least one semi-metal compound or at least one mixed-metal compound with at least one liquid, one solid or one gas, in which process it can be advantageous if water, alcohol or an acid, for example, is used as the liquid, ice as the solid or steam as the gas, or if at least one combination of these liquids, solids or gases is used. It can also be advantageous to add the compound to be hydrolyzed to alcohol or an acid or a combination of these liquids before hydrolysis. As the compound to be hydrolyzed there is preferably hydrolyzed at least one metal nitrate, one metal chloride, one metal carbonate, one metal alcoholate compound or at least one semi-metal alcoholate compound, especially preferably at least one metal alcoholate compound, one metal nitrate, one metal chloride, one metal carbonate or at least one semi-metal alcoholate compound chosen from the compounds of the elements Ti, Zr, Al, Si, Sn, Ce and Y or of the lanthanoids and actinoids, such as titanium alcoholates, for example titanium isopropylate, silicon alcoholates, zirconium alcoholates, or a metal nitrate, such as zirconium nitrate.
It can be advantageous to perform the hydrolysis of the compounds to be hydrolyzed with at least half the molar ratio of water, steam or ice relative to the hydrolyzable group of the hydrolyzable compound.
The hydrolyzed compound can be peptized with at least one organic or inorganic acid, preferably with a 10 to 60% organic or inorganic acid, especially preferably with a mineral acid chosen from sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid and nitric acid or a mixture of these acids.
There can be used not only sols prepared as described hereinabove, but also commercial sols such as titanium nitrate sol, zirconium nitrate sol or silica sol.
It can be advantageous if at least one inorganic component with a particle size of 1 to 10,000 nm is suspended in at least one sol. Preferably there is suspended an inorganic component containing at least one compound chosen from metal compounds, semi-metal compounds, mixed metal compounds and metal mixed compounds with at least one of the elements of Group 3 to Group 7, or at least one mixture of these compounds. Especially preferably there is suspended at least one inorganic component containing at least one compound comprising the oxides of the subgroup elements or the elements of Group 3 to Group 5, preferably oxides chosen from the oxides of the elements Sc, Y, Ti, Zr, Nb, Ce, V, Cr, Mo, W, Mn, Fe, Co, B, Al, In, Tl, Si, Ge, Sn, Pb and Bi, examples being Y2O3, ZrO2, Fe2O3, Fe3O4, SiO2, Al2O3. The inorganic component can also contain aluminosilicates, aluminum phosphates, zeolites or partly exchanged zeolites, such as ZSM-5, Na ZSM-5 or Fe ZSM-5 or amorphous microporous mixed oxides, which can contain up to 20% nonhydrolyzable organic compounds, such as vanadium oxide silica glass or alumina silica methylsilicon sesquioxide glasses. Preferably the proportion by weight of the suspended component amounts to 0.1 to 500 times the hydrolyzed compound used.
Freedom from cracks in the composite material according to the invention can be optimized by appropriate choice of the particle size of the suspended compounds as a function of the size of the pores, holes or interstices of the porous permeable support, and also by the layer thickness of the composite material according to the invention as well as by the proportional ratio of sol, solvent and metal oxide.
In order to increase freedom from cracks in the use of a mesh fabric with a mesh width of 100 xcexcm, for example, there can preferably be used suspensions which contain a suspended compound with a particle size of at least 0.7 xcexcm. In general, the ratio of particle size to mesh or pore size should range from 1:1000 to 50:1000. The composite material according to the invention can preferably have a thickness of 5 to 1000 xcexcm, especially preferably 50 to 150 xcexcm. The suspension of sol and compounds to be suspended preferably has a ratio of sol to compounds to be suspended ranging from 0.1:100 to 100:0.1, preferably from 0.1:10 to 10:0.1 parts by weight.
The suspension present on or in or on and in the support can be solidified by heating this composite to 50 to 1000xc2x0 C. In a special alternative embodiment of the process according to the invention, this composite is exposed to a temperature of 50 to 100xc2x0 C. for 10 minutes to 5 hours. In a further special embodiment of the process according to the invention, this composite is exposed to a temperature of 100 to 800xc2x0 C. for 1 second to 10 minutes.
The heat treatment of the composite according to the invention in the manner can be accomplished by means of heated air, hot air, infrared radiation, microwave radiation or electrically generated heat. In a special embodiment of the process according to the invention it can be advantageous if the heat treatment of the composite is performed using the support material for electrical resistance heating. For this purpose the support can be connected to a current source via at least two contacts. With the current turned on, the support becomes heated in proportion to amperage of the current source and amplitude of the output voltage, and the suspension present in and on its surface can be solidified by this heating.
In a further particularly preferred embodiment of the process according to the invention, the solidification of the suspension can be accomplished in that the suspension is applied on or in or on and in a preheated support and thus is solidified directly after application.
According to the invention the ion-conducting composite material can be obtained by using at least one polymer-bound Brxc3x6nstedt acid or base for making the composite material. Preferably the ion-conducting composite material can be obtained by using at least one sol, which contains polymer particles bearing fixed charges or polyelectrolyte solutions. It can be advantageous if the polymers bearing fixed charges or the polyelectrolytes have a melting or softening point below 500xc2x0 C. Preferably there are used as polymers bearing fixed charges or as polyelectrolytes sulfonated polytetrafluoroethylene, sulfonated polyvinylidene fluoride, aminolyzed polytetrafluoroethylene, aminolyzed polyvinylidene fluoride, sulfonated polysulfone, aminolyzed polysulfone, sulfonated polyether imide, aminolyzed polyether imide or a mixture thereof. The proportion of the polymers bearing fixed charges or of the polyelectrolytes in the sol being used ranges preferably from 0.001 wt % to 50.0 wt %, especially preferably from 0.01% to 25%. The polymer can undergo chemical and physical or chemical or physical modification during production and processing of the ion-conducting composite material.
By adding to the sol used for making the composite material a small quantity of a polymer which bears acid or basic groups and also has a certain thermal stability, such as Nafion(copyright), there can be made an ion-conducting permeable composite material with particular properties. During solidification of the material, the polymer melts. It surrounds the respective inorganic particles as a thin film, and so there are formed at the surfaces pores which have an lonogenic character and are very suitable for ion conduction. Because the heat treatment is brief, only very slight degradation of the charges in the polymer takes place. If the polymer proportion is increased during production, the layers on the particles become progressively larger, until the point is reached at which the pores are completely filled. Thereby there is achieved directly in one process step a nonporous ion-conducting composite material supported by the porous support. Its ion conductivity is reduced by the quantity of particles, but it has better mechanical strength than the starting material. This is particularly important for applications at higher temperatures.
The ion-conducting composite material can also be obtained, however, by using, during production of the composite material, a sol which contains at least one ion-conducting material or at least one material which exhibits ion-conducting properties after a further treatment. Preferably there are added to the sol materials which lead to formation of inorganic ion-conducting layers on the interior and/or exterior surfaces of the particles contained in the composite material.
According to the invention, the sol can be obtained by hydrolyzing at least one metal compound, at least one semi-metal compound or at least one mixed-metal compound or a combination of these compounds with a liquid, a gas and/or a solid. Preferably water, steam, ice, alcohol or acid or a combination of these compounds is used as the liquid, gas and/or solid for hydrolysis. It can be advantageous to add the compound to be hydrolyzed to alcohol and/or to an acid before hydrolysis. Preferably there is hydrolyzed at least one nitrate, chloride, carbonate or an alcoholate of a metal or semi-metal. Especially preferably the nitrate, chloride, carbonate or alcoholate to be hydrolyzed is a compound of the elements Ti, Zr, V, Mn, W, Mo, Cr, Al, Si, Sn and/or Y.
It can be advantageous if a compound to be hydrolyzed bears nonhydrolyzable groups in addition to hydrolyzable groups. Preferably an alkyltrialkoxy or dialkyldialkoxy or trialkylalkoxy compound of the element silicon is used as such a compound to be hydrolyzed.
The ion-conducting components on the interior and/or exterior surfaces are then incompletely converted hydroxyl groups, which are bound in the crystal lattice and therefore permit exclusively surface diffusion, without being affected themselves. If zeolites or xcex2-aluminosilicates are now also added as particles to the sol, there is obtained an almost homogeneous composite material which exhibits almost homogeneous ion-conduction properties.
According to the invention, there can be added to the sol for making the composite material at least one acid or base which is soluble in water and/or alcohol. Preferably there is added an acid or base of the elements Na, Mg, K, Ca, V, Y, Ti, Cr, W, Mo, Zr, Mn, Al, Si, P or S.
The sol used for making the ion-conducting composite material in the manner according to the invention can also contain nonstoichiometric metal, semi-metal or nonmetal oxides or hydroxides, generated by changing the oxidation number of the corresponding element. The change in oxidation number can be achieved by reaction with organic compounds or inorganic compounds or by electrochemical reactions. Preferably the change of oxidation number is achieved by reaction with an alcohol, aldehyde, sugar, ether, olefin, peroxide or metal salt. Examples of compounds which can change oxidation number in this way are Cr, Mn, V, Ti, Sn, Fe, Mo, W or Pb.
According to the invention it can be advantageous if there are added to the sol substances which lead to formation of inorganic ion-conducting structures. Examples of such substances can be zeolite and/or xcex1-aluminosilicate particles.
As an example, there can therefore be made in the manner according to the invention an ion-conducting permeable composite material constructed almost exclusively from inorganic substances. In this connection the sol composition is a relatively important factor, since a mixture of different hydrolyzable components must be used. These individual components must be carefully matched to one another as regards their hydrolysis rate. It is also possible to generate the nonstoichiometric metal oxide hydrate sols by appropriate redox reactions. The metal oxide hydrates of the elements Cr, Mn, V, Ti, Sn, Fe, Mo, W or Pb are readily accessible in this way. The ion-conducting compounds on the interior and exterior surfaces are then different partly hydrolyzed or nonhydrolyzed oxides, phosphates, phosphides, phosphonates, stannates, plumbates, chromates, sulfates, sulfonates, vanadates, tungstates, molybdates, manganates, titanates, silicates or mixtures of these of the elements Al, K, Na, Ti, Fe, Zr, Y, Va, W, Mo, Ca, Mg, Li, Cr, Mn, Co, Ni, Cu or Zn or mixtures of these elements.
In a further preferred embodiment of the process according to the invention, already existing permeable ion-conducting or non-ion-conducting composite materials can be treated with ion-conducting materials or with materials which exhibit ion-conducting properties after a further treatment. Such composite materials can be commercial permeable materials or composite materials, or else composite materials as described, for example, in PCT/EP98/05939. It is also possible, however, to use composite materials obtained by the process described hereinabove.
According to the invention, there are obtained ion-conducting permeable composite materials by treating, with at least one ion-conducting material or with at least one material which exhibits ion-conducting properties after a further treatment, a composite material which has a pore width of 0.001 to 5 xcexcm and which exhibits or does not exhibit ion-conducting properties.
The treatment of the composite material with at least one ion-conducting material or at least one material which exhibits ion-conducting properties after a further treatment can be accomplished by impregnating, dipping, brushing, rolling on, doctoring on, spraying or other coating techniques. After the treatment with at least one ion-conducting material or at least one material which exhibits ion-conducting properties after a further treatment, the composite material is preferably heat-treated. Especially preferably the heat treatment is performed at a temperature of 100 to 700xc2x0 C.
Preferably the ion-conducting material or the material which exhibits ion-conducting properties after a further treatment is applied on the composite material in the form of a solution with a solvent proportion of 1 to 99.8%. According to the invention, there can be used as the material for making the ion-conducting composite material polyorganylsiloxanes which contain at least one ionic constituent. The polyorganylsiloxanes can contain among other substances polyalkylsiloxanes and/or polyarylsiloxanes and/or further constituents.
It can be advantageous if at least one Brxc3x6nstedt acid or base is used as the material for making the ion-conducting composite material. It can also be advantageous if at least one trialkoxysilane solution or suspension containing acid and/or basic groups is used as the material for making the ion-conducting composite material. Preferably at least one of the acid or basic groups is a quatemary ammonium or phosphonium group or an alkylsulfonic acid, carboxylic acid or phosphonic acid group.
By means of the process according to the invention, therefore, it is possible, for example, subsequently to provide an already existing permeable composite material with an ionic finish by treatment with a silane. For this purpose a 1 to 20% solution of this silane is prepared in a water-containing solution, and the composite material is dipped therein. As the solvent there can be used aromatic and aliphatic alcohols, aromatic and aliphatic hydrocarbons and other common solvents or mixtures. Advantageously there can be used ethanol, octanol, toluene, hexane, cyclohexane and octane. After the adhering liquid has dripped off, the impregnated composite material is dried at about 150xc2x0 C. and can be used as an ion-conducting permeable composite material either directly or after a plurality of subsequent steps of coating and drying at 150xc2x0 C. Both silanes bearing cationic groups and silanes bearing anionic groups are suitable for this purpose.
It can also be advantageous if the solution or suspension for treating the composite material also contains acid or basic compounds and water in addition to a trialkoxysilane. Preferably the acid or basic compounds comprise at least one Brxc3x6nstedt or Lewis acid or base known to those skilled in the art.
According to the invention, however, the composite material can also be treated with solutions, suspensions or sols which contain at least one ion-conducting material. This treatment can be performed one time or repeated several times. With this embodiment of the process according to the invention there are obtained layers of one or more similar or different partly hydrolyzed or nonhydrolyzed oxides, phosphates, phosphides, phosphonates, sulfates, sulfonates, vanadates, tungstates, molybdates, manganates, titanates, silicates or mixtures of these of the elements Al, K, Na, Ti, Fe, Zr, Y, Va, W, Mo, Ca, Mg, Li, Cr, Mn, Co, Ni, Cu or Zn or mixtures of these elements.
Ion-conducting permeable composite materials can be used in numerous processes. By virtue of the acid sites on the interior and/or exterior surfaces they are capable of catalyzing numerous reactions. Examples thereof are esterification and acetalization reactions, as well as rearrangements and numerous other acid-catalyzed reactions.
The ion-conducting composite materials according to the invention can also be used in fuel cells. This possibility is particularly important in view of the better thermal stability compared with polymer membranes. Heretofore the operating range of proton exchange membrane fuel cells has been limited to a maximum temperature of 120 to 130xc2x0 C. by the use of Nafion as the membrane. Higher temperatures lead to a severe decrease of the ion conductivity of Nafion. In the said fuel-cell type, a higher operating temperature leads to a distinct improvement of service life, since the problem of catalyst poisoning by carbon monoxide is suppressed. In addition, a direct methanol fuel cell can be achieved more easily thereby.
The ion-conducting composite materials according to the invention are extremely suitable as ion-exchange membranes in electrolysis, membrane electrolysis and electrodialysis cells. They satisfy virtually all requirements imposed on an ion-exchange membrane for these applications. Such requirements would be good permselectivity, high ion flux and small thickness of the membrane.
Since ion-conducting layers are simultaneously highly hydrophilic, ion-conducting permeable composite materials according to one of claims 1 to 20 can be used in separation of substances by pervaporation and vapor permeation in the case of problems involving selective separation of water from organic substances. A main area of application in this case is solvent drying, where the currently used membrane materials are limited to a few solvents (ethanol and similar substances) and to temperatures below 100xc2x0 C. because of the swelling behavior of the support polymers and because of the relatively low thermal stability of these polymers.
The greater thermal stability of the ion-conducting permeable composite materials according to the invention also permits use thereof for high-temperature applications of pervaporation, such as the treatment of partial streams during rectification. The enormous technical advantage under these conditions is that the partial streams to be treated no longer have to be passed through heat exchangers, but instead can be sent directly to the pervaporation membrane at the respective process temperature (which can be as high as 250xc2x0 C.).